Foot-and-mouth disease (FMD) is one of the most virulent and contagious diseases affecting farm animals. This disease is endemic in numerous countries in the world, especially in Africa, Asia and South America. In addition, epidemic outbreaks can occur periodically. The presence of this disease in a country may have very severe economic consequences resulting from loss of productivity, loss of weight and milk production in infected herds, and from trade embargoes imposed on these countries. The measures taken against this disease consist of strict application of import restrictions, hygiene controls and quarantine, slaughtering sick animals and vaccination programs using inactivated vaccines, either as a preventive measure at the national or regional level, or periodically when an epidemic outbreak occurs.
FMD is characterized by its short incubation period, its highly contagious nature, the formation of ulcers in the mouth and on the feet and sometimes, the death of young animals. FMD affects a number of animal species, in particular cattle, pigs, sheep and goats. The agent responsible for this disease is a ribonucleic acid (RNA) virus belonging to the Aphthovirus genus of the Picornaviridae family (Cooper et al., 1978, Intervirology 10, 165-180). At present, at least seven types of foot-and-mouth disease virus (FMDV) are known: the European types (A, O and C), the African types (SAT1, SAT2 and SAT3) and an Asiatic type (Asia 1). Numerous sub-types have also been distinguished (Kleid et al., 1981, Science 214, 1125-1129).
FMDV is a naked icosahedral virus of about 25 nm in diameter, containing a single-stranded RNA molecule consisting of about 8500 nucleotides, with a positive polarity. This RNA molecule comprises a single open reading frame (ORF), encoding a single polyprotein containing, inter alia, the capsid precursor also known as protein P1 or P88. The protein P1 is myristylated at its amino-terminal end. During the maturation process, the protein P1 is cleaved by the protease 3C into three proteins known as VP0, VP1 and VP3 (or 1AB, 1D and 1C respectively; Belsham G. J., Progress in Biophysics and Molecular Biology, 1993, 60, 241-261). In the virion, the protein VP0 is then cleaved into two proteins, VP4 and VP2 (or 1A and 1B respectively). The mechanism for the conversion of the proteins VP0 into VP1 and VP3, and for the formation of mature virions is not known. The proteins VP1, VP2 and VP3 have a molecular weight of about 26,000 Da, while the protein VP4 is smaller at about 8,000 Da.
Many hypotheses, research routes, and proposals have been developed in an attempt to design effective vaccines against FMD. Cao et al. (Antiviral Research, 2013, 97:145-153; Veterinay Microbiology, 2014, 168:294-301) reported the design of specific epitope proteins with immunogenicity against FMDV challenge. A synthetic polypeptide corresponding to the fusion of one T epitope and two B epitopes from Asia serotype was proved to induce a protective response (Ren et al., Vaccine, 2011, 29:7960-7965).
Currently, the only vaccines on the market comprise inactivated virus. Concerns about safety of the FMDV vaccine exist, as outbreaks of FMD in Europe have been associated with shortcomings in vaccine manufacture (King, A. M. Q. et al., 1981, Nature, 293: 479-480). The inactivated vaccines do not confer long-term immunity, thus requiring booster injections given every year, or more often in the event of epidemic outbreaks. In addition, there are risks linked to incomplete inactivation and/or to the escape of virus during the production of inactivated vaccines (King, A. M. Q., ibid).
Recently the E2 subunit of the dehydrogenase multienzyme complexes was used as a scaffold to produce HIV-1 proteins (Caivano et al., 2010, Virology, 407:296-305; Krebs et al., PLOS One, 2014, DOI:10.1371/journal.pone.0113463; Schiavone et al., 2012, Int. J. Mol. Sci., 13:5674-5699). Pyruvate dehydrogenase (PDH) complexes are multifunctional enzymes that contain three essential enzymes: a thiamine-dependent pyruvate decarboxylase (E1), a dihydrolipoyl acetyltransferase (E2), and a flavoprotein dihydrolipoyl dehydrogenase (E3) (Lengyel et al., Structure, 16:93-103, 2008). It was discovered that sixty copies of the E2 polypeptide from the PDH complex of Bacillus stearothermophilus assemble to form a pentagonal dodecahedral scaffold, and the scaffold may be modified to present foreign peptides and proteins on its surface (Domingo et al., 2001, J. Mol. Biol., 305:259-267). Dalmau et al. (Biotechnology and Bioengineering, 101(4):654-664, 2008) described E2 mutants of PDH that were optimized for expression in E. coli. D′Apice et al. (Vaccine, 25:1993-2000, 2007) discussed the expression of a T helper epitope in three delivery vehicles: the filamentous bacteriophage fd, the E2 protein from the PDH complex and the protein CotC.
Considering the susceptibility of animals, including humans, to FMDV, a method of preventing FMDV infection and protecting animals is essential. Accordingly, there is a need for an effective, safe and easy to produce vaccine against FMDV.